Fri·Jul 27, 2018Friday·July 27, 2018

1. 01*

   Measurements of the chiral magnetic effect with background isolation in 200 GeV Au+Au collisions at STAR

   Jie Zhao (for the STAR collaboration)🇺🇸

   Using two novel methods, pair invariant mass ($m_{inv}$) and comparative measurements with respect to reaction plane (${\Psi }_{\mathrm{RP}}$) and participant plane (${\Psi }_{\mathrm{PP}}$), we isolate the possible chiral magnetic effect (CME) from backgrounds in 200 GeV Au+Au collisions at STAR. The invariant mass method identifies the resonance background contributions, coupled with the elliptic flow ($v_2$), to the charge correlator CME observable ($\Delta \gamma$). At high mass ($m_{inv}>1.5$ GeV/$c^2$) where resonance contribution is small, we obtain the average $\Delta \gamma$ magnitude. In the low mass region ($m_{inv}<1.5$ GeV/$c^2$), resonance peaks are observed in $\Delta \gamma$($m_{inv}$). An event shape engineering (ESE) method is used to model the background shape in $m_{inv}$ to extract the potential CME signal at low $m_{inv}$. In the comparative method, the ${\Psi }_{\mathrm{RP}}$ is assessed by spectator neutrons measured by ZDC, and the ${\Psi }_{\mathrm{PP}}$ by the 2${}^{nd}$-harmonic event plane measured by the TPC. The $v_2$ is stronger along ${\Psi }_{\mathrm{PP}}$ and weaker along ${\Psi }_{\mathrm{RP}}$; in contrast, the magnetic field, mainly from spectator protons, is weaker along ${\Psi }_{\mathrm{PP}}$ and stronger along ${\Psi }_{\mathrm{RP}}$. As a result, the $\Delta \gamma$ measured with respect to ${\Psi }_{\mathrm{RP}}$ and ${\Psi }_{\mathrm{PP}}$ contain different amounts of CME and background, and can thus determine these two contributions. It is found that the possible CME signals with background isolation by these two novel methods are small, on the order of a few percent of the inclusive $\Delta \gamma$ measurements.

   nucl-exhep-exhep-phnucl-thNPA(2019)·23 citations
2. 02*

   Quarkonium production in nuclear collisions

   Rongrong Ma🇺🇸

   In these proceedings, an overview of recent quarkonium measurements in nuclear collisions carried out at both RHIC and LHC is presented. In p+p collisions, despite theoretical progresses made in understanding the production mechanisms for quarkonia, a complete picture is still yet to be achieved. In p+A collisions where measurements are done to quantify the cold nuclear matter effects, significant suppression of quarkonium production is observed for low transverse momentum region at both forward- and mid-rapidities. Furthermore, results from A+A collisions show the interplay of dissociation and regeneration contributions for charmonium at different collision energies, while a correspondence between the suppression level and the binding energy is observed for bottomonium family. Comparisons to experimental data provide stringent tests to model calculations, and help constrain the temperature of the deconfined medium created in heavy-ion collisions.

   nucl-exNPA(2019)·3 citations
3. 03*

   First Observation of $P$-odd $\gamma$ Asymmetry in Polarized Neutron Capture on Hydrogen

   D. Blyth🇺🇸 · J. Fry🇺🇸 · N. Fomin🇺🇸 · R. Alarcon🇺🇸 · L. Alonzi🇺🇸 · E. Askanazi🇺🇸 · S. Baeßler🇺🇸 · S. Balascuta🇺🇸 · L. Barrón-Palos🇲🇽 · A. Barzilov🇺🇸 · J.D. Bowman🇺🇸 · N. Birge🇺🇸 and 52 other authors

   We report the first observation of the parity-violating 2.2 MeV gamma-ray asymmetry $A_{\gamma }^{np}$ in neutron-proton capture using polarized cold neutrons incident on a liquid parahydrogen target at the Spallation Neutron Source at Oak Ridge National Laboratory. $A_{\gamma }^{np}$ isolates the $\Delta I=1$, \mbox{${}^3{S}_1\to {}^3{P}_1$} component of the weak nucleon-nucleon interaction, which is dominated by pion exchange and can be directly related to a single coupling constant in either the DDH meson exchange model or pionless EFT. We measured $A_{\gamma }^{np}=[-3.0\pm 1.4(stat)\pm 0.2(sys)]\times 10^{-8}$, which implies a DDH weak $\pi NN$ coupling of $h_{\pi }^1=[2.6\pm 1.2(stat)\pm 0.2(sys)]\times 10^{-7}$ and a pionless EFT constant of $C^{{}^3{S}_1{\to }^3{P}_1}/C_0=[-7.4\pm 3.5(stat)\pm 0.5(sys)]\times 10^{-11}$ MeV${}^{-1}$. We describe the experiment, data analysis, systematic uncertainties, and the implications of the result.

   nucl-exhep-exPRL(2018)·52 citations
4. 04*

   Pion-kaon femtoscopy in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV measured with ALICE

   Ashutosh Kumar Pandey (for the ALICE Collaboration)🇮🇳

   Femtoscopic correlations between charged pions and kaons for different charge combinations are measured in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV with ALICE at the LHC. The three-dimensional pion-kaon ($\pi -\mathrm{K}$) correlation functions and double ratios in the out-side-long pair rest frame are studied in different centrality bins. The $\pi -\mathrm{K}$ femtoscopic source size parameter ($R_{\mathrm{out}}$) and emission asymmetry (${\mu }_{\mathrm{out}}$) are extracted. It is observed that the average source size of the system and the emission asymmetry between pions and kaons increase from peripheral to central events.

   ↳ hep-exnucl-exNPA(2019)·4 citations
5. 05*

   Reduced hadronic uncertainty in the determination of $V_{ud}$

   Chien-Yeah Seng🇨🇳 · Mikhail Gorchtein🇩🇪 · Hiren H. Patel🇺🇸 · Michael J. Ramsey-Musolf🇺🇸

   We analyze the universal radiative correction ${\Delta }_R^V$ to neutron and superallowed nuclear $\beta$ decay by expressing the hadronic $\gamma W$-box contribution in terms of a dispersion relation, which we identify as an integral over the first Nachtmann moment of the $\gamma W$ interference structure function $F_3^{(0)}$. By connecting the needed input to existing data on neutrino and antineutrino scattering, we obtain an updated value of ${\Delta }_R^V=0.02467(22)$, wherein the hadronic uncertainty is reduced. Assuming other Standard Model theoretical calculations and experimental measurements remain unchanged, we obtain an updated value of $|V_{ud}|=0.97366(15)$, raising tension with the first row CKM unitarity constraint. We comment on ways current and future experiments can provide input to our dispersive analysis.

   ↳ hep-phnucl-exnucl-thPRL(2018)·290 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.